# CVE-2026-45905: xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

> A race condition in the Linux kernel's XFRM ICMP handling can trigger a kernel warning and potential denial of service.

- **Severity:** Medium 4.7 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 May 2026
- **Updated:** 27 May 2026
- **Also known as:** BELL-CVE-2026-45905, DEBIAN-CVE-2026-45905, GHSA-qfvj-mcf4-fgpg, ROOT-OS-DEBIAN-11-CVE-2026-45905, ROOT-OS-UBUNTU-2204-CVE-2026-45905, ROOT-OS-UBUNTU-2404-CVE-2026-45905, UBUNTU-CVE-2026-45905

## What is CVE-2026-45905?

CVE-2026-45905 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

xfrm: fix ip_rt_bug race in icmp_route_lookup reverse path

icmp_route_lookup() performs multiple route lookups to find a suitable
route for sending ICMP error messages, with special handling for XFRM
(IPsec) policies.

The lookup sequence is:
1. First, lookup output route for ICMP reply (dst = original src)
2. Pass through xfrm_lookup() for policy check
3. If blocked (-EPERM) or dst is not local, enter "reverse path"
4. In reverse path, call xfrm_decode_session_reverse() to get fl4_dec
   which reverses the original packet's flow (saddr<->daddr swapped)
5. If fl4_dec.saddr is local (we are the original destination), use
   __ip_route_output_key() for output route lookup
6. If fl4_dec.saddr is NOT local (we are a forwarding node), use
   ip_route_input() to simulate the reverse packet's input path
7. Finally, pass rt2 through xfrm_lookup() with XFRM_LOOKUP_ICMP flag

The bug occurs in step 6: ip_route_input() is called with fl4_dec.daddr
(original packet's source) as destination. If this address becomes local
between the initial check and ip_route_input() call (e.g., due to
concurrent "ip addr add"), ip_route_input() returns a LOCAL route with
dst.output set to ip_rt_bug.

This route is then used for ICMP output, causing dst_output() to call
ip_rt_bug(), triggering a WARN_ON:

 ------------[ cut here ]------------
 WARNING: net/ipv4/route.c:1275 at ip_rt_bug+0x21/0x30, CPU#1
 Call Trace:
  <TASK>
  ip_push_pending_frames+0x202/0x240
  icmp_push_reply+0x30d/0x430
  __icmp_send+0x1149/0x24f0
  ip_options_compile+0xa2/0xd0
  ip_rcv_finish_core+0x829/0x1950
  ip_rcv+0x2d7/0x420
  __netif_receive_skb_one_core+0x185/0x1f0
  netif_receive_skb+0x90/0x450
  tun_get_user+0x3413/0x3fb0
  tun_chr_write_iter+0xe4/0x220
  ...

Fix this by checking rt2->rt_type after ip_route_input(). If it's
RTN_LOCAL, the route cannot be used for output, so treat it as an error.

The reproducer requires kernel modification to widen the race window,
making it unsuitable as a selftest. It is available at:

  https://gist.github.com/mrpre/eae853b72ac6a750f5d45d64ddac1e81

Weakness: CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-45905?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-45905?

Apply the vendor's patch.

## Is CVE-2026-45905 being exploited?

There is no known exploitation of CVE-2026-45905 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-45905 and fix it if it is affected.

What it is: CVE-2026-45905 is a medium-severity vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-45905 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-45905/ (Markdown: https://insights.sbomify.com/CVE-2026-45905/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-45905
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-45905
- OSV: https://osv.dev/vulnerability/CVE-2026-45905

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-45905/
Summaries are generated and may contain mistakes; the official description above is the record.